FRANKFURT, Germany (AP) — Michael Schumacher's doctors have started trying to wake up the former Formula One Champion from the medically induced coma he's been in since a skiing accident last month, his manager said Thursday.

The 45-year-old Schumacher suffered serious head injuries when he fell and hit the right side of his head on a rock in the French resort of Meribel on Dec. 29. The seven-time F1 champion has been in an induced coma in Grenoble University Hospital since then, although his condition stabilized following surgery after initially being described as critical.

"Michael's sedation is being reduced in order to allow the start of the waking up process which may take a long time," Schumacher's manager, Sabine Kehm, said in a statement. Schumacher was being kept artificially sedated and his body temperature was lowered to between 34 and 35 degrees Celsius (93.2 and 95 degrees Fahrenheit), to reduce swelling in the brain, reduce its energy consumption and allow it to rest.

Kehm said she was only providing an update now on Schumacher's condition to clarify media leaks, and that no further details would be provided. French newspaper l'Equipe first reported on Wednesday that doctors had started trying to wake up Schumacher.

Pahl warned that if Schumacher hasn't recovered enough to wake up on his own, doctors might need to put him back in the coma.

"It could be that swelling in his brain hasn't come to an end yet so they might need to increase the medications again," he said. Pahl said that wasn't uncommon in patients with brain injuries and that sometimes it took several attempts to bring someone out of an induced coma.

Brain experts said it will be fundamental to determine whether Schumacher was aware of his surroundings and could respond to basic commands from doctors, like raising his hand.

"This is a test to see what his function is like," said Dr. Anthony Strong, an emeritus chair in neurosurgery at King's College London. He said that once the sedatives wear off, Schumacher's doctors would see if he can breathe on his own and if he responds to mild pain stimulus, like gentle pressing on his eyebrows.

"Doctors will want to see if he can say 'hello,' if he probe his recollection of events and to see if he can recognize family members and remember his own identity," Strong said. If Schumacher doesn't respond to their voice, they will also look to see if he tries to pull out any of the tubes in him or rip the dressing off his wounds — which would be a sign that he is aware of where he is.

Still, experts said it would likely be months before Schumacher's prognosis becomes clear — and that lasting brain damage was a possibility.

"If he pulls through, he may not be the man he was," said Dr. Tipu Aziz, head of neurosurgery at Oxford University. "Given the length of time he's been in (intensive care), he has clearly had a very severe head injury," he said. "It's too early to know how intact he will be, but I would guess there is going to be some kind of lasting damage."

Schumacher earned universal acclaim for his uncommon and sometimes ruthless driving talent, which led to a record 91 race wins. He retired from Formula One in 2012 after garnering an unmatched seven world titles. His accident happened on a family vacation in the Alps as Schumacher was skiing with his 14-year-old son.

PHOTOS: SCHUMACHER'S CAREER IN PHOTOS

Michael Schumacher poses with the new Ferrari Formula One race car 248 F1 during the official presentation at the Mugello racetrack in Scarperia, central Italy, in this Jan. 24, 2006 file photo. The Formula One great who sustained severe head injuries in a ski accident in late 2013, is no longer in a coma and has left the French hospital where he was being treated since the accident, his spokeswoman said on June 16, 2014. Tony Gentile, Reuters

Michael Schumacher leaps in the air on the podium watched by Victorian state premier, Steve Bracks (below), after winning the Australian Formula One Grand Prix in Melbourne in 2004. Greg Wood, AFP/Getty Images

Schumacher speeds down the course in Madonna di Campiglio, Italy, in 2004. He was in the northern Italian mountain resort to take part in the annual meeting between Ferrari and the media. Luca Bruno, AP

From left to right, professor Jean-Francois Payen, professor Stephan Chabardes, assistant director Marc Penaud, professor Emmanuel Gay, and professor Gerard Saillant talk during a press conference at the Grenoble hospital, in the French Alps, where former seven-time Formula One champion Michael Schumacher is being treated after sustaining a head injury during a ski accident. Laurent Cipriani, AP

A cap with handwritten Dutch writing that reads 'get well soon, number one' is fixed near the entry of the Michael Schumacher cart-center on Dec. 30, 2013 in Kerpen, Germany. Juergen Schwarz, Bongarts/Getty Images